What program are you using to determine that your CPU is not throttling? I see you have CPU-Z open. Here is a good example of why you can not depend on CPU-Z MHz to determine if your CPU is throttling or not.
http://www.overclock.net/t/1438732/event-viewer-vs-intels-etu-for-reporting-thermal-throttling#post_...CPU-Z can show you 2800 MHz but that might be meaningless if the CPU is being throttled internally to a fraction of its rated speed.
You mentioned that you tried ThrottleStop. Can you try running ThrottleStop again and post a screen shot of how you have ThrottleStop set up? I would also suggest clicking on the Log File option in ThrottleStop before this starts happening so you have a clear record of exactly what your CPU is doing. Let's make sure that your CPU really is performing at its Intel rated speed.
You can Copy and Paste your ThrottleStop log file data to
www.pastebin.com and then post a link here so I can have a look. It is possible that the GPU speed has dipped way down because the CPU is being throttled so badly that it can't keep up.